That makes the most sense, I bet if you purchased a AP at a ticket booth it would say roughly the same thing. The card is just to get you in ONE TIME so you can get your official AP.
What you purchased is a one-day ticket that you exchange for an AP on the day that you use it. Sometime during that day, you must visit the AP processing center to get photographed and have your AP issued to you. One year after that day becomes the expiration date of your new AP.
Have bicycle, will ride. Finished 2012 with 10,089 miles, 683 hours, and 482,000 feet of elevation gain. So far in 2013: 4068 miles, 272 hours, 267K feet.